Fuel injection systems

ABSTRACT

A fuel injection system which injects fuel intermittently and in which the periods of time for which fuel is injected are determined by the rate of flow of a control fluid. This rate of flow is in turn controlled by an air valve located in the engine air intake to produce a control depression and adjustable to maintain that depression substantially constant. Preferably, the control fluid is air flowing from atmosphere into the control depression region, and the system preferably also includes a mechanism for adjusting the periods of time for which fuel is injected to compensate for variations in the control depression.

United States Patent 1 1 Jackson 1 1 FUEL INJECTION SYSTEMS [75] Inventor: Harold Ernest Jackson, Elburton,

England [73] Assignee: Petrol Injection Limited, Plymouth,

Devon, England [22] Filed: May 24, 1971 [21] Appl. No.: 146,135

[30] Foreign Application Priority Data May 26, 1970 Great Britain ..25,304/70 Feb. 26, 1971 Great Britain ..5,550/7l [52] U.S. Cl. ..l23/32 EA, 123/139 E, 123/119, 123/139 AW, 123/140 MC [51] Int. Cl. ..F02m 51/00 [58] Field of Search 123/32 EA, 119 R, 139 E,

139 Aw,123/'139 B6, 140 MP, 140 MC [56] References Cited UNITED STATES PATENTS 2,8933%? 5 7719 5 9 llaefn erfjfllilf.123F397? 1 Jan. 23, 1973 2,856,910 10/1958 Goodridge ..l23/l39 AW 3,482,558 12/1969 Casey et al.... .....123/l39 AW 3,575,147 4/1971- Harrison ..l23l32 EA 3,650,258 3/1972 Jackson ..l23/139 AW Primary Examiner--Laurence M. Goodridge Attorneyl-lolcombe, Wetherill & Brisebois [57] ABSTRACT A fuel injection system which injects fuel intermittently and in which the periods of time for which fuel is injected are determined by the rate of flow of a control fluid. This rate of flow is in turn controlled by an air valve located in the engine air intake to produce a control depression and adjustable to maintain that depression substantially constant. Preferably, the con- 1 trol fluid is air flowing from atmosphere into the control depression region, and the system preferably also includes a mechanism for adjusting the periods of time for which fuel is injected to compensate for variations in the control depression.

42 Claims, 12 Drawing Figures PATENTEDJANZB 197a SHEET UlUF 10 PATENTED JAN 2 3 I975 SHEET U3UF 10 PATENTED JAN 23 I975 SHEET U 4 HF 10 PATENTEDJAN 23 I973 SHEET U5UF10 PATENTED JAN 23 I975 SHEET 07UF 10 PATENTED JAN 2 3 I975 SHEET 08 0F 10 FIG. 8c.

PATENTEDJM|23 I975 3.712.275

SHEET lOUF 1O Q Q m FUEL INJECTION SYSTEMS This invention relates to fuel injection systems for internal combustion engines and, in particular, to systems in which fuel is injected intermittently rather than continuously.

The present invention provides a fuel injection system for an internal combustion engine, including at least one fuel injector nozzle and at least one interrupter valve connected to control fuel flow through the nozzle(s); an air valve mechanism which includes an air valve located in the engine air intake path to produce a control pressure differential over a region of the air intake path, and which is operable in response to a variation in the control pressure differential from a desired value to adjust the air valve to return the control pressure differential to the desired value; a control fluid flow line to which the air valve is coupled whereby the rate of flow of control fluid through the line varies in response to adjustment of the air valve, and an interrupter valve control mechanism which is cyclically operable to actuate the interrupter valve(s) and then, after a period of time in each cycle determined by the rate of flow of the control fluid, to terminate actuation of the interrupter valve(s).

The control fluid may be air or it may be fuel within the system.

If the control fluid is air, then the control fluid flow line may be connected to the control pressure differential region. The control fluid flow line may, for example, be connected to feed air into the control pressure differential region from an air supply source (for example, the atmosphere).

If, on the other hand, the control fluid is fuel, then the control fluid flow line may be connected to receive fuel from'and return fuel to the fuel supply source of the injector nozzle(s).

The air valve may be coupled to an adjustable flow restrictor in the control fluid flow line.

The interrupter valve control mechanism may include a frequency control which is cyclically operable to actuate the interrupter valve(s) at a frequency which may be constant or dependent on engine speed. In an embodiment of the invention, the frequency control also operates a How control valve connected in the control fluid flow line and operable to change the flow resistance of the line and thereby produce a variation in control fluid pressure, at a point in the flow line, at a rate determined by the rate of flow of control fluid. In this embodiment, the interrupter valve control mechanism also includes a pressure-responsive control which is operable to terminate actuation of the interrupter valve(s) in response to a predetermined value of control fluid pressure at the said point in the flow line. The pressure-responsive control may, for example, include a fluid pressure-responsive electrical switch hav ing a fluid-pressure responsive element exposed to the control fluid pressure at the said point in the control fluid flow line.

When the system includes a pressure-responsive control as defined above, the said predetermined value of control fluid pressure is preferably adjustable. The pressure-responsive control may, for example, also be responsive to a biasing pressure whereby variations in the biasing pressure adjust the said predetermined value. The biasing pressure may vary with the control pressure difierential whereby the said predetennined value is adjusted in response to variations in the control pressure differential to compensate for variations in the rate of flow of the control fluid resulting from those variations. Alternatively, or in addition, the system may include at least one enrichment valve operable to adjust the biasing pressure and thereby adjust the period of time for which the or each, interrupter valve is actuated.

The air valve mechanism may include a fluid pressure-operated servomechanism to which the air valve is coupled, and a sensing valve responsive to a variation in the control pressure differential to adjust the servomechanism: the air valve mechanism may, for example, take one of the forms disclosed in the Complete Specification of our copending U.S. Pat. applications Ser. No. 31,315, now abandoned and Ser. No. 3,316, now U.S. Pat. No. 3,650,258, filed Apr. 23, 1970. Alternatively, the air valve may be an eccentricallymounted butterfly valve with the air valve mechanism including restoring means acting on the air valve in opposition to the control pressure differential.

By way of example, systems constructed in accordance with the invention will be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a system constructed in accordance with the invention;

FIG. 2 is a block circuit diagram of a component of the system shown in FIG. 1;

FIG. 3 is a cross-section through a fuel injector device which is suitable for use in the system shown in FIG. 1;

FIG. 4*is a view of one of the components of FIG. 1;

FIG. Sis a view on the line V--V of FIG. 4;

FIGS. 6, 7 and 8 are diagrams of other systems constructed in accordance with the invention;

FIG. 9 is a block circuit diagram of a component of the system shown in FIG. 8, and

FIG. 10 illustrates a modification of the system shown in FIG. 8;

In the system shown in FIG. 1, fuel is drawn from a tank I by any suitable form of pump 2 (for example an electrically-driven gear pump) and passed to a supply conduit 3. Injector supply pipes 4 are connected to deliver fuel from the supply conduit 3 to respective injector devices 5 (only one of which is shown in FIG. I) and fuel not passed to the injector devices is returned to the tank 1 via a relief valve 6 and a return conduit 7.

The injector devices 5 are positioned to discharge fuel into'the induction system of the internal combustion engine downstream of the customary throttle valve: each injector device may, for example, be positioned to discharge fuel into the individual intake branch of a respective engine cylinder. The injector devices 5 are air-bled devices each including a solenoid-operated interrupter valve and will be described in greater detail below. Operation of each injector device 5 to discharge fuel is controlled by an interrupter valve control mechanism in the form of an electronic switching unit 8 to which the injector device is electrically connected as indicated at 9 in FIG. 1. The switching unit 8, which will be described in greater detail below, operates to control the injector devices 5 in dependence on engine air intake as will also be described below.

The relief valve 6 includes two chambers 51 and 52 separated by a resilient diaphragm 53. The supply conduit 3 and the return conduit 7 both communicate with the chamber 51 but communication between the conduits is controlled by the diaphragm 53 which is biased by an adjustable spring 54 towards a seating 55 to prevent fuel flow from the supply conduit 3 to the return conduit 7. Fuel pressure in the supply conduit 3 acts on the diaphragm 53 and when this pressure is sufficient to overcome the spring 54, the diaphragm moves away from the seating 55 to permit fuel flow to the return conduit 7. In this way, the relief valve 6 functions to maintain a substantially constant fuel pressure (determined by the spring 54) in the supply conduit 3.

The engine air intake conduit is shown diagrammatically at 10 in FIG. 1 and in greater detail in FIGS. 4 and 5, and feeds air to the engine in the direction left to right as seen in the drawings. The air intake conduit 10 includes the customary manually-operated throttle valve 1 1 and, located upstream of the throttle valve, an air valve 12. The air valve 12 produces a control depression in the intake conduit 10 between the air valve 12 and throttle valve 11 when the engine is in operation and forms part of a mechanism which, as will be described below, operates in response to a variation in the control depression to adjust the air valve to return the control depression to a desired value, and thereby maintain the control depression substantially constant. An air control line 13 communicates with the control depression region of the air intake conduit 10 and is connected, through a pressure-responsive airtiming switch 14 to a normally-closed solenoidoperated flow control valve 15. The solenoid valve 15, when open, vents the air control line 13 -to atmosphere. The air-timing switch 14 is electrically connected to the switching unit 8 as indicated at 16 in FIG. 1 and also to the operating solenoid of the valve 15. The purpose of the control line 13, the air-timing switch 14 and the solenoid valve will be described below. The intake conduit 10 also includes an enrichment switch 212 which 'is positioned downstream of the throttle 11 and is also connected to the switching unit 8. The purpose of the enrichment switch 212 will be described below.

The air valve 12 is a butterfly valve eccentrically mounted on a spindle 17. When the engine is operating, air flow through the intake conduit 10 will result in a depression being created between the air valve 12 and the throttle valve 11, and the eccentric mounting of the air valve is such that the air valve tends to open under the action of this depression. The air valve mechanism also includes a spring (not shown) which exerts a restoring (that is, closing) force on the air valve 12 and the characteristics of this spring are so chosen, having regard to the eccentricity of the spindle 17, that the position 'of the air valve 12 varies with the air flow through the conduit 10 in such a manner that the depression produced between the air valve 12 and the throttle valve 1 1 remains substantially constant (for cxample at 1" Hg).

The spindle 17 on which the air valve 12 is mounted also carries a cam 18 (located outside the intake conduit 10 as shown in FIGS. 4 and 5) which cooperates with a follower 19 mounted on one end of a lever 20 (also located outside the intake conduit). A needle valve 21 is mounted on the other end of the lever 20 and forms an adjustable flow restrictor controlling the degree of communication between the air control line 13 and the conduit 10 through passages 40 formed in an extension 41 of the intake conduit body as shown in FIGS. 4 and 5. A screw 42 bears against the lever 20 as shown in FIG. 5 and enables the position of the needle valve 21 to be adjusted for any position of the air valve 12. A stop 43 (FIG. 4) engageable with an extension 44 of the throttle valve spindle 45 limits movement of the latter to prevent jamming, and the air intake conduit 10 also includes a conventional idling control 46 which bypasses the throttle 1 1 and is operable to admit air to the conduit 10 under idling conditions.

The air-timing switch 14 has two chambers 22, 23 separated by a pressure-responsive element in the form of a resilient diaphragm 24. The chamber 22 is connected in the air control line 13 and the chamber 23 is vented at 25 to atmosphere. The diaphragm 24 carried an electrical contact 26 connected to an external terminal 27 and engageable with a second electrical contact 28 which is located in the chamber 22 and is connected to an external terminal 29. The external terminals 27, 29 are connected by the leads 16 to the switching unit 8. A spring 30 located in the chamber 23 biases the diaphragm 24 to a position in which the contact 26 is out of engagement with the contact 28.

The air timing switch is so connected to the solenoid valve 15 that movement of contact 26 into engagement with contact 28 causes the valve 15 to open and vent the air control line to atmosphere. The solenoid valve 15 will, however, only close in response to a control signal from the switching unit 8, as will be described below, and does not close in response to movement of contact 26 out of engagement with contact 28.

The system, as so far described, functions as follows. When the engine is operating, a control depression is created in the air intake conduit 10 between the air valve 12 and the throttle valve 11 and this control depression is maintained substantially constant by the action of the air valve 12 as described above. The needle valve 21 takes up a position which depends on the position of the air valve 12, so that any variation in engine air intake which results in adjustment of the air valve to maintain the control depression substantially constant is accompanied also by adjustment of the needle valve 21 to vary the degree of communication between the air control line 13 and the air intake conduit 10.

The control depression in the air intake conduit 10 causes air to be drawn throughthe needle valve 21 from the air control line 13 and this (assuming the nole-v noid valve V1! is closed) reduces the pressure in the chamber 22 ot the air-timing switch 14. As a result, the diaphragm 24 is pulled against the action of the spring 30 and the contact 26 comes into engagement with the contact 28 thereby completing the circuit between the leads 16 to the control unit 8 and also causing the solenoid valve 15 to open. Opening of the valve 15 vents the air control line 13 to atmosphere so that the pressure in chamber 22 of the air-timing switch 14 rises and the diaphragm 24 returns to its original position thereby breaking the circuit between the leads 16. The solenoid valve 15, however, remains open until a closure signal is received from the switching unit 8.

The switching unit 8 will be described in greater detail below and for the present it is sufficient to state that the unit includes a frequency control which generates electrical closure signals at a rate dependent on engine speed, for example 1 closure signal on every other engine revolution. It is also for the present sufficient to state that the air-timing switch 14 forms part of a pressure-responsive control and is so connected to the switching unit 8 that closure of the air-timing switch contacts 26, 28 causes an electrical pulse to be applied to the operating solenoids of the injector devices 5, to open the injector devices so that fuel is discharged into the cylinder intakes. Generation of a closure signal by the frequency control of the switching unit 8, on the other hand,'terminates the electrical pulse applied to the injector devices 5 so that the latter close and discharge of fuel ceases.

It will be seen from the above that although closing of the injector devices 5 is dependent on engine speed, opening of the injector devices (being governed by the air-timing switch 14) is dependent on engine air intake. That is, the point of time in each cycle, i.e. each period of two engine revolutions, at which the injector devices 5 open is determined by engine air intake and the length of time in each cycle for which the injectors are open is determined by engine air intake and also by the cycle time which in turn is determined by the engine speed.

That is,

where T, is the length of time in each cycle for which the injectors are open Q,, is the engine air intake unit of time n is the engine speed C is a constant. Accordingly, the fuel flow to the engine per unit of time is given by Q,- where where K is a constant. That is, the fuel flow to the engine per unit of time is independent of engine speed and is dependent solely on engine air intake. In general, if engine air intake increases then adjustment of the air valve 12 to maintain a substantially constant control depression between the air valve 12 and the throttle valve 11 will cause the needle valve 21 to open further, and air to be drawn more quickly from the air-control line 13. The result of this will be that the air-timingswitch contacts 26, 28"will come into engagement more quickly so that the injector devices 5 will open at an earlier point in each period of two engine revolutions and will, accordingly remain open for a greater length of time and discharge a greater amount of fuel. That is, an increase in engine air intake will be accompanied by an increase in the amount of fuel discharged by the injector devices 5.

The construction of one suitable form of injector device 5 is illustrated in FIG. 3. The device has a fuel inlet 140 which, in use, is connected to an injector supply pipe 4 (FIG. 1). The inlet 140 communicates,

via a passage 141, with the interior of a tubular interrupter valve member 142 which, in turn, communicates through ports 143 in the wall of the valve member with a chamber 144. A spring 145 seated on an end portion of the interrupter valve member 142 biases the valve member against a seating 146, in which position communication between the chamber 144*and a fuel tube 147 is cut-off by the valve member. The fuel tube 147 is a small diameter stainless steel tube and is aligned with an outlet orifice 148 in an outer jacket 149 surrounding the tube. The space between the tube 147 and the jacket 149 is vented through ports 150. Movement of the valve member 142 is controlled by a solenoid 151 within which the valve member is partly located. The valve member 142, or at least that portion of the valve member which is located within the solenoid is formed of a magnetizable material so that energization of the solenoid 151 moves the valve member away from the seating 146 and allows fuel to flow into the fuel tube 147 and to be discharged through the outlet orifice 148. As fuel is being discharged, air is drawn into the jacket 149 through the ports 150. In use of the injector device, thesolenoid 151 is connected to the switching unit 8 by the leads 9 (FIG. 1).

It will be appreciated, however, that the injector devices 5 need not be of the type shown in FIG. 3: they could, for example, be of the type described in copending US. application Ser. No. 179,961, filed Sept. 13, 1971.

A block circuit diagram of the switching unit 8 is shown in FIG. 2. The various components of the unit are conventional and will, therefore, not be described in great detail. The contacts of the air-timing switch 14 are shown in FIG. 2 and, as in FIG. 1, carry the reference numerals 26, 28. The operating solenoids of the injector devices 5 are also shown and, as in FIG. 3, carry the reference numeral 151, while the operating solenoid of the valve 15 (FIG. 1) is indicated by the reference numeral 151A.

The closure signals which are applied by the switching unit 8 to the solenoids 151, 151A are derived from the circuit of the ignition coil '220 of the engine, including the conventional contact breaker 221 and spark plugs 222. A transformer 201 (shown also in FIG. 1) monitors the ignition pulses so that a pulse is produced in the secondary coil of the transformer on each operation of the contact breaker 221. That is, for a four cylinder, four-stroke engine, 4 pulses will be produced in the secondary coil of the transformer for every 2 revolutions of the engine. These pulses are applied, through a conventional pulse-limiting circuit 202, to a conventional pulse-shaping circuit 203 from which the pulses (now in the form of square waves) are applied to a series of two conventional bistable multivibrators 204, 205. Each of these multivibrators functions to generate one output pulse in response to every two input pulses, so that the output of the combination is one pulse for every 2 revolutions of the engine.

The output of the multivibrators 204, 205 is applied to a pulse switching circuit 210 which, in turn, is connected to power output stages 206A, 206B and 207. Power stages 206A and 2068 each serve one pair of injector solenoids 151 while the power stage 207 serves the valve solenoid 151A, and the switching circuit 210 isolates these power stages from the binary stages 204,

205. The circuit shown in FIG. 2 also includes a pulseextension circuit 211 with which is associated the throttle-controlled enrichment switch 212 mentioned above. The purpose of circuit 211 and switch 212 will be described below: they are not essential to the operation of the switching unit 8 and could be omitted.

For the present, only the basic switching unit will be considered, that is, excluding the pulse-extension circuit 211 and the enrichment switch 212. During operation of the engine, the components 201 to 205 of the switching unit, forming the frequency control, function as described above to generate one electrical pulse for every 2 engine revolutions and these engine-speed dependent pulses are applied to the solenoids 151, 151A through the associated power stages 206A, 2068 and 207. Each engine-speed dependent pulse causes the injector devices and the solenoid valve to close so that fuel injection ceases. Closure of the solenoid valve 15 is followed by operation of the air-timing switch 14 as described above during which the air-timing switch contacts 26, 28 close. Referring to FIG. 2, it will be seen that closure of the contacts 26, 28 connects the output of the pulse switching circuit 210 to earth through line 213: this results in a pulse being applied to the solenoids 151, 151A, which causes the interrupter valves of the injector devices 5, and the solenoid valve 15 to open. Fuel injection accordingly commences, and the air-timing switch contacts 26, 28 reopen but the injectors 5 and solenoid valve 15 remain open until the next engine-speed dependent pulse is generated by components 201 to 205. In other words, closure of the injector devices 5 occurs in response to signals generated (by the frequency control components 201 to 205) in dependence on engine speed, whereas the injector devices open in response to signals generated (by the pressure-responsive control including air-timing switch 14) in dependence on engine air intake.

The pulse-extension circuit 211 and fuel enrichment switch 212 form an enrichment control and are included to provide the engine with a comparatively greater amount of fuel when the throttle valve 11 is fully opened. The fuel enrichment switch 212 is located, as mentioned above, in the air intake conduit 10 downstream of the throttle valve 11 (see FIG. 1) and is normally open so that the pulse-extension circuit 211 is disconnected from the remaining components of the switching unit 8. The switch 212 is so positioned, however, that it is closed by the throttle valve 11 when the latter is moved to the fully-open position. The pulse-extension circuit 211 is a conventional monostable vibrator circuit which, when switch 212 is closed, delays the application of a closure signal (generated by the components 201 to 205) to the injector solenoids 151 by an amount determined by the time constant of the circuit 211. The injector devices 5 accordingly remain open for a greater length of time and the engine receives a correspondingly greater amount of fuel.

Although the enrichment-switch 212 has been described above as being actuated by the throttle valve 11, it could, alternatively, be a pressure-responsive switch exposed to inlet manifold vacuum and adjusted to close when that vacuum reaches a value corresponding to the throttle 11 being fully opened.

Another system constructed in accordance with the invention is illustrated in FIG. 6. This system is generally similar to that shown in FIG. 1 and corresponding components carry the same reference numerals. As in FIG. 1, the system includes a plurality of injector devices 5 to which fuel is delivered by a pump 2 from a tank 1 at a pressure determined by a relief valve 6, and operation of the injector devices is controlled by a switching unit 8. The system also includes an air control line 13 from which air is drawn into the control depression region of the engine air intake conduit 10 at a rate determined by a needle valve 21 coupled to an air valve 12 located in the intake conduit 10 upstream of the throttle valve 11. As in FIG. 1 the air control line 13 includes a pressure-responsive air-timing switch 14 and a solenoid-operated flow control valve 15, both electrically-connected to the switching unit 8, and the injector devices 5 open and close together with the solenoid-operated valve 15.

The system differs from that shown in FIG. 1 in the following respects:

a. the system includes an additional solenoidoperated flow control valve 60 which is connected in the air control line 13 on the intake conduit side of the air-timing switch 14 and is so connected to the switching unit that the valve 60 closes as the valve 15 opens, and vice versa;

b. the switch contacts 26, 28 are located in chamber 23, rather than chamber 22, of the air-timing switch 14, whereby the contacts open, rather than close, under the influence of an increasing depression chamber 22;

c. chamber 22 of the air-timing switch 14 is connected to the solenoid-operated valve 15 through a calibrated restrictor 61 whereby, when the valve 15 is open, atmospheric air leaks into chamber 22 at a decreased rate determined by the restrictor.

In. addition, although the frequency control of the switching unit 8 receives 4 pulses from the ignition coil circuit 200 for every 2 engine revolutions as in FIG. 1, two of these are used as operating pulses to perform switching operations rather than only one as in the system shown in FIG. 1.

The operation of the system over two engine revolutions is as follows, it being assumed initially that the solenoid-operated valve 15 is closed. Under these conditions, the solenoid-operated valve 60 is open and, as in FIG. 1, the injector devices 5 are closed. The control depression created in the intake conduit 10 between the air valve 12 and throttle valve 11 causes air to be drawn from the control line 13 through the needle valve 21 at a rate determined by the position of the air valve 12. This, in turn, causes diaphragm 24 in the airtiming switch 14 to be pulled downwardly, as shown in the drawing, to increase the separation between the contacts 26 and 28 until the first operating pulse is generated by the frequency control of the switching unit 8. This pulse closes the valve 60 and opens the valve 15,'and it also opens the interrupter valves of the injector devices 5 so that fuel injection commences. Since the valve 60 is closed, the air-timing switch 14 is now cutoff from the intake conduit 10 but is vented to atmosphere through the open valve 15. Atmospheric air accordingly leaks into chamber 22 of the switch at a rate determined by the calibrated restrictor 61, allowing the diaphragm to move gradually to close the switch contacts 26, 28. Closure of the switch contacts 26, 28

acts to close the solenoid valve 15 and also the injector devices so that fuel injection ceases. Both solenoid valves and 60 then remain closed until the second operating pulse is generated by the frequency control of the switching unit 8: this pulse opens the valve 60 and the cycle then repeats on the next two engine revolutions. It will be seen therefore that in this system closure of the injector devices 5 occurs in response to signals generated (by the pressure responsive control including air-time switch 14) in dependence on engine air intake, whereas the injector devices open in response to signals generated (by the frequency control of switching unit 8) in dependence on engine speed.

It will be appreciated that the circuit diagram of the switching unit 8 for the system shown in FIG. 6 will be generally similar to that shown in FIG. 2 but will require modification to achieve the switching operations described above. The necessary modifications are, however, conventional having regard to the required switching operations and need not be described.

The system shown in FIG. 7 of the drawings differs from those shown in FIGS. 1 and 6 in that the air control line 13 of the latter systems is replaced by a fuel control line 70 which includes a device 71 operable to pressurize fuel in the control line in dependence on the control depression between the air valve 12 and the throttle valve 11 in the air intake conduit 10. The fuel control line 70 is, however, to some extent similar to the air control line 13 shown in FIG. 6 in that it includes a pressure-responsive timing switch 72 (although, in this case, one that is fuel-operated) and two solenoid-operated flow control valves 15 and 60, the former being associated with a calibrated restrictor 61.

The system includes a fuel pump 2 which delivers fuel from a tank 1 to the pressurizing device 71 from which fuel passes to the fuel control line 70 and also, through a pressure control valve 73, to a chamber 74 in the pressurizing device, from which the plurality of injector devices 5 are fed. The pressure in chamber 74, and hence the pressure at which fuel is supplied to the injector devices 5 is maintained at a substantially constant value by the relief valve 6 connected in the fuel return line 7 from the injector devices to the tank 1. The relief valve 6 and pressurizing device 71 are shown in FIG. 7 as forming a single component, but this is not essential.

Operation of the injector devices 5 to discharge fuel is controlled, as in the systems described above, by the switching unit 8 to which, as in FIG. 6, the timing switch 72 and the solenoid-operated valves 15 and 60 are also connected.

The pressure control valve 73 is formed by a valve member 75 located in the chamber 74 and co-operating with a seating 76.-The valve member 75 is mounted at one end ofa control rod 77 which extends through a seal 78 into a further chamber 79 formed in the pressurizing device 71. The chamber 79 is connected by a conduit 80 to the control depression region of the air intake conduit 10, and is separated by adiaphragm 81 from a chamber 82 which is vented to atmosphere. The control rod 77 is capable of rocking movement in the seal 78 and is coupled to the diaphragm 81 which thereby controls movement of the pressure control valve member 75.

From the pressurizing device 71, fuel in the control line passes through a variable restriction formed by a needle valve 21 which, as in the systems shown in FIGS. 1 and 6 is coupled to the air valve 12 through a lever 20 and a cam and cam follower 18, 19. The fuel then passes to the solenoid valve 60, timing switch 72, solenoid valve 15 and calibrated restrictor 61, and then returns to the fuel tank 1.

The system operates as follows, over two engine revolutions. Normally, as described with reference to FIG. 1, the air valve 12 adjusts to maintain a substantially constant depression in the intake conduit 10 between the valves 12 and 11. This depression is applied through conduit 80 to the diaphragm 81 of pressurizing device 71 and, through rod 77, determines the position of the valve member fuel supplied by the pump 2 then divides between the injector devices 5 and the control line 70 to an extent determined by the position of the valve member. As described above with reference to FIGS. 1 and 6, the needle valve 21 adopts a position determined by the air valve 12 and accordingly varies fuel flow through the control line 70 in dependence on engine air intake.

Assuming, initially, that the solenoid-operated valve 15 is closed but' that valve 60 is open, it will be seen that fuel in control line 70 will flow through the needle valve 21 and into chamber 22 of the timing switch 72 causing the pressure in chamber 22 to increase. The pressure increase causes the switch contacts 26, 28 to separate at a rate dependent on engine air intake and this continues until an operating pulse is generated by the frequency control of the switching unit 8 which, as in the system shown in FIG. 6, receives 4 pulses from the ignition coil circuit of the engine for every 2 engine revolutions, two of these pulses being used as operating pulses to perform switching operations. The first operating pulse closes the solenoid-operated valve 60 and opens the valve 15: the pulse also opens the interrupter valves of the injector devices 5 so that fuel injection commences. Since valve 60 is closed, the timing switch 72 is now cut-off from the needle valve 21, but the opening of the valve 15. allows fuel to leak from chamber 22 of the switch back to the fuel tank 1 at a rate determined by the calibrated restrictor 61. The pressure in chamber 22 accordingly decreases and the switch contacts 26, 28 move into engagement. Closure of the switch 26, 28 causes the solenoid-operated valve 15 to close, and also the injector devices 5 so that fuel injection now ceases. Both solenoid-operated valves 15, 60 are now closed and remain so until the second operating pulse is generated by the frequency control of the switching unit 8: this pulse opens the valve 60 and the cycle then repeats on the next two engine revolutions. It will be seen that the switching operations are similar to those described above for the system shown in FIG. 6'and that a similar form of switching unit 8 would be employed. As in FIG. 6, closure of the injector devices 5 occurs in response to signals generated (by pressure-responsive control including the timingswitch 72) in dependence on engine air intake, whereas the injector devices open in response to signals generated, (by the frequency control of the switching unit 8) in dependence on engine speed.

Provided the control depression in the intake conduit 10 remains substantially constant, the position of the pressure control valve member 75 will remain substantially unaltered and the fuel pressure in the control line 70 will remain substantially constant. The pressurizing device 71 does, however, come into operation during sudden acceleration to ensure that the engine immediately receives an enriched fuel/air mixture. On sudden acceleration, the depression between the valves 12 and 11 in the intake conduit 10 may rise suddenly before the position of the air valve is adjusted to return the depression to the substantially constant value. The increased depression is effective immediately on the diaphragm 81 of the pressurizing device 71 to move the valve member 75 to a closed position with the result that the fuel pressure in the control line 70 rises until equilibrium is restored. The increased fuel pressure causes the contacts 26, 28 of the timing switch 72 to move apart more rapidly with the result that the injector devices remain open for an extended length of time and the engine receives more fuel. When the position of the air valve 12 has adjusted to restore the control depression in the intake conduit to the substantially constant value, the fuel pressure in the control line 70 also reverts to its original value, but the new position of the air valve is, of course, accompanied by adjustment of the needle valve 21.

Another system constructed in accordance with the invention is illustrated in FIG. 8. This system is similar to that shown in FIG. 1 and corresponding components carry the same reference numerals. As in FIG. 1, the system includes a tank (not shown) from which fuel is drawn by any suitable form of pump (not shown) and passed to a supply conduit 3. Injector supply pipes 4 are connected to deliver fuel from the supply conduit 3 to injector devices 5 and excess fuel is returned to the tank via a relief valve 6 and a return conduit 7.

The injector devices 5 are air-bled devices each including a solenoid-operated interrupter valve, as in FIG. 1. The injector devices are positioned to discharge fuel into the induction system of the internal combustion engine downstream of the customary throttle valve and are controlled by an electronic switching unit 8 to which each device is electrically connected as indicated at 9. The switching unit 8 operates, as in FIG. 1, to control the injector devices 5 in dependence on engine air intake as will be described below.

The relief valve 6 functions as described above with reference to FIG. 1 to maintain a substantially constant fuel pressure in the supply conduit 3.

The engine air intake conduit 10 feeds air to the engine in the direction left to right as seen in FIG. 8 and includes the customary manually-operated throttle valve 11. Upstream of the throttle valve 1 1, an air valve 12 is located in the intake conduit and produces a control depression between the air and throttle valves when the engine is in operation. An air control line 13 communicates with the control depression region of the intake conduit 10 through a metering valve (not shown) -and is connected, through the lower chamber 22 of a pressure-responsive air timing switch 14 to a solenoid-operated flow control valve 15 which, when energized, vents the air control line 13 to atmosphere through a restrictor 13a. Both the air timing switch 14 and the valve 15 are electrically connected to the switching unit 8 as indicated at 14a and 15a respectively. A compensation line 300 including a fixed restrictor 321 connects the control depression region of the intake conduit 10 to the upper chamber 23 of the air tim ing switch 14, this chamber being vented to atmosphere through a fixed restrictor 301.

The system also includes a cold start enrichment valve 302, a fuel cut-off switch 303 and a power enrichment valve 304, all of which will be described in greater detail below.

The air valve 12 is a butterfly valve which, unlike the air valve of the systems described above, is centrally mounted on its spindle 17. The spindle 17 is coupled, through a linkage 305 to the diaphragm 306 of a vacuum-operated servomechanism 307. The diaphragm 306 defines two chambers 308, 309 within the servomechanism, and a passageway 310 from the control depression region of the air intake conduit 10 communicates directly with the chamber 309 and, through a restrictor 31 l with the chamber 308.

Mounted on the servomechanism is a vacuum sensing valve 312 which includes a diaphragm 313 biased by a spring 314 towards a seating 315. The diaphragm 313 is exposed to the depression in the control depression region of the intake conduit 10, through the passageway 310, and controls communication between the chamber 308 of the servomechanism and atmosphere through a passage 316 and a vent 317.

The spindle 17 of the air valve 12 also carries a cam 318 with which cooperates a follower 319 biased by a spring 320. The action of the spring 320 is to urge the air valve 12 into the closed position. The follower 319 operates the metering valve, mentioned above, which forms an adjustable flow restrictor controlling communication between the air control line 13 and the control depression region of the air intake conduit 10. This metering valve, which is not shown, may be of any suitable type, for example that described in British Pat. No. l,098,82l comprising a tubular valve member which is located within a sleeve and includes a V-slot registering with an aperture in the sleeve to define a metering orifice the area of which can be varied by relative rotation between the valve member and the sleeve.

When the engine is operating, air flow through the intake conduit 10 results in a control depression being created between the air valve 12 and the throttle valve 11. If the control depression is larger than a predetermined value, the diaphragm 313 of the vacuum sensing valve 312 is pulled away from the seating 315, thereby connecting the chamber 308 of the servomechanism 307 to atmosphere. The restrictor 311 ensures that air leaks from the chamber 308 only gradually so that the pressure .in the chamber rises and causes the servomechanism diaphragm 306 to move and open the air valve 12,- thereby decreasing the control depression. If, on the other hand, the control depression is too small then the sensing valve diaphragm 313 remains against the seating 315 and the absence of a pressure differential across the servomechanism diaphragm 306 allows the air valve to move towards the closed position under the action of the spring 320 to increase the con trol depression. In this way, the control depression is maintained at a substantially constant value, a suitable value being I" Hg. The restricted connection 311 between the chamber 308 and the control depression region of the intake conduit 10 slows down movement of the servomechanism diaphragm 306 in response to operation of the sensing valve 312 to prevent hunting but, in the event of a sudden change in the control depression, the restricted connection 311 in combination with the direct connection to the chamber 309 ensures that a pressure differential is produced immediately across the diaphragm 306 to urge the air valve 12 in the appropriate direction to restore the control depression to the predetermined value.

Adjustment of the air valve 12 is accompanied by movement of the cam 318 and follower 319 resulting in adjustment of the metering valve controlling the degree of communication between the air control line 13 and the intake conduit 10.

The upper and lower chambers 23, 22 of the air timing switch 14 are separated by a pressure-responsive element in the form of a resilient diaphragm 24 carrying an electrical contact 26 connected to an external terminal 27. The diaphragm 24 is biased, by a spring 30 located in the lower chamber 22, towards a position in which the contact 26 engages a second electrical contact 28 which is located in the upper chamber 23 and is connected to an external terminal 29. The terminals 27, 29 form part of a pressure-responsive control portion of the switching unit 8 and are connected to the unit 8 by the leads 14a.

The switching unit 8 also includes a frequency control which generates electrical control signals at a rate dependent on engine speed. These control signals, which are derived from the conventional contact breaker 221 as will be described below are applied to the injector devices and to the solenoid valve 15 and cause the injector devices and the valve to open, thereby allowing fuel to flow to the engine cylinders and atmospheric air to enter the chamber 22 of the timing switch 14. When the injector devices 5 and the solenoid valve 15 are closed, the control depression in the intake conduit causes air to be drawn from the chamber 22 at a rate determined by the setting of the metering valve (not shown) and, since the solenoid valve is closed, the diaphragm 24 is drawn away from the contact 28 against the action of the spring 30. This continues until a signal is generated by the frequency control portion of the switching unit 8, opening the injector devices 5 and also opening the solenoid valve 15 to allow atmospheric air to enter the chamber 22 at a rate determined by the restrictor 13a. The diaphragm 24 then moves back towards the contact 28 until the contacts 26, 28 of the pressure-responsive control engage, causing the injector devices 5 and the solenoid valve 15 to close again. Accordingly, the length of time in each engine cycle for which the injector devices 5 are open to discharge fuel is determined by the distance between the diaphragm 24 and the contact 28 when a signal is generated by the frequency control portion of the switching unit 8 and this, in turn, is determined by the position of the air valve 12 and, hence, by engine air intake.

The system as so far described functions in a similar manner to the system shown in FIG. 1. It has been found, however, that although the servomechanism 307 and signal valve 312 respond rapidly to changes in the control depression in the air intake conduit 10 and, by adjusting the air valve, restore the control depression to the chosen value, the transient conditions can, by affecting operation of the timing switch 14, have a disadvantageous effect on the relationship between fuel delivery and engine air intake. The line 300 is provided to compensate for transient variations in the control depression by providing a restoring bias for the timing switch diaphragm 24, which at all times is a fixed proportion of the control depression. The effect of the line 300 can be seen from the following: Suppose the chosen value of the control depression is V" Hg and the force exerted by the spring 30 on the diaphragm 24 is equivalent to x" Hg. Then, in the absence of the line 300, the air drawn from the chamber 22 of the timing switch in one ending cycle is and the air drawn into the chamber 22 in one engine cycle is where a, a are consfiints 'and'if, eisia'ie'saama ly-the cycle time and the time in the cycle for which the solenoid valve 15 is open. Accordingly, in the absence of the line 300,

If, however, the line 300 is present, a depression kV (determined by the restrictors 301, 321 in line 300) is created in the chamber 23 of the timing switch. This depression assists the spring 30 so that, in the presence of the line 300 where b,, b and k are constants. It can be seen from this that the line 300 reduces the effect on t (and hence on the quantity of fuel injected) of any variation in the control depression V from the normal, substantially constant, value. If the chosen normal value of the control depression is l Hg then an appropriate value for the force of spring 30 is 0.23" Hg and for the depression in chamber 23 of the timing switch is 0.46 V Hg. Under these conditions a variation in the control depression Vof as much as 10 percent results in a variation no greater than 1.7 percent in the length of time for which the solenoid valve 15 is open.

As mentioned above, the system also includes a cold start enrichment valve 302. This valve comprises two variable restrictors 330, 331 both coupled to a control member 332 which may be manually or automatically operated. The restrictor 330 is connected in a line 333 from the upper chamber 23 of the timing switch 14 to an overriding pressure source (in this case the atmosphere) and the restrictor 331 is connected in a bypass line 334 from the control depression region to the downstream side of the throttle valve 11. Under cold start conditions, the control member 332 is rotated to open the restrictors 330, 331 thereby admitting air to the chamber 23 of the timing switch and allowing air from the control depression region to by-pass the throttle valve 11. As a result, the bias urging the timing switch diaphragm 24 towards the contacts-closed position is reduced, so that the injector devices 5 remain open for a greater length of time, and, simultaneously, the air flow to the engine is increased.

The power enrichment valve 304 also functions to modify the depression in timing switch chamber 23, but under full-load rather than cold start conditions. The

valve 304 includes a diaphragm 340 coupled through a push-button 343 to a valve member 344 controlling a connection through restrictors 345, 346 between the chamber 23 and a vent 341 to an overriding pressure source (in this case the atmosphere). The diaphragm 340 is exposed, through a line 342 to inlet manifold vacuum. Normally, the valve member 344 is in the closed position but, under full-load conditions (that is, when throttle valve 11 is fully open and inlet manifold vacuum is low), the diaphragm 340 acts through the button 343 to push the valve member to an open position thereby admitting air to the timing switch chamber 23 and increasing the length of time for which the injector devices are open.

The fuel cut-off switch 303 is provided to reduce engine exhaust emission during deceleration conditions. The switch is controlled by a diaphragm 350 exposed on one side to inlet manifold vacuum through a line 351 and on the other side to atmosphere through a vent 352. The diaphragm 350 carries'an electrical contact 353 and is biased towards a position in which the contact 353 engages a further contact 354. The contacts 353, 354 are connected through external terminals 355 to the switching unit 8 and are normally in engagement. Under engine deceleration conditions, however, inlet manifold vacuum is high and the switch diaphragm 350 is pulled to a contacts-open position, which, through the switching unit 8 breaks the electrical circuit to the injector devices 5 to cut-off the fuel supply to the engine.

A block circuit diagram of the switching unit 8 is shown in FIG. 9 from which it can be seen that the unit is generally similar to that shown in FIG. 2, and corresponding components carry similar reference numerals. The air timing switch is indicated, as in FIG. 8, by the reference 14 and the fuel cut-off switch by the reference 303, while the operating solenoids of the injector devices 5 and valve 15 are indicated at 151 and 151A respectively. The engine-speed dependent control signals which are applied by the frequency control portion of the switching unit 8 to the solenoids 151, 151A are derived from the circuit of the ignition coil 220 including the conventional contact breaker 221 (shown also in FIG. 8) and spark plugs 222. A transformer 201 monitors the ignition pulses to produce, in the case of a four-cylinder four-stroke engine, four output pulses for every two engine revolutions. These pulses are applied through conventional pulse-limiting and pulse-shaping circuits 202, 203 to a counter which devises the number of pulses by the number of engine cylinders: in the case of a four-cylinder, four stroke engine the counter comprises a series of two conventional bistable multivibrators 204, 205 and produces one output pulse for every two engine revolutions. The output of the counter is connected, through the fuel cut-off switch 303, to a bistable switching circuit 210 which is connected, through an amplifier stage indicated generally at 223, to a power switching circuit 206 controlling the solenoids 151, 151A. The input of the bistable switching circuit 210 is also connected to the airtiming switch 14 as shown.

During operation of the engine, the fuel cut-ofi switch 303 is normally closed and electrical pulses are applied to the solenoids 151, 151A from the counter 204, 205 of the frequency control portion of the unit 8 at the rate of one pulse for every two engine revolutions. Each of these pulses switches the bistable circuit 20 to open the injector devices 5 and the solenoid valve 15 and is then followed by closure of the .air timing switch 14 in the pressure-responsive control portion of the unit 8, which causes the injector devices 5 and the solenoid valve 15 to close. Under engine deceleration conditions, the cut-ofi' switch 303 opens and breaks the electrical circuit to the solenoids 151, 151A.

The amplifier stage 223 of the switching unit comprises a conventional monostable circuit 224 and high current amplifier 225 providing a high voltage pulse of short duration which opens the injector devices 5 and solenoid valve 15 rapidly, and a conventional low current amplifier 226 providing a low voltage pulse which holds the injector devices 5 and solenoid valve 15 in the open condition until closure of the timing switch 14 occurs. The stepped nature of the pulse applied to the power switching circuit 206 enables power consumption to be reduced and it will be appreciated that a similar arrangement could be incorporated in the switching units 8 of the systems shown in FIGS. 1 6 and 7.

FIG. 10 illustrates a modification of the system shown in FIG. 8. In this modification, the power enrichment diaphragm valve 304 is replaced by a power enrichment check valve 360 connected to the air timing switch 14 and the air intake conduit 10 as shown in FIG. 10. The remaining components of the system are unchangedand are not shown in FIG. 10. The check valve 360 has an inlet 361 connected, through a restrictor 362 to a line 363 at a point intermediate two restrictors 364, 365. The line 363 joins the air intake conduit 10 downstream of the throttle valve 11 and is connected to an overriding pressure source (in this case, the'atmosphere) at 366. The outlet 367 of the check valve communicates with the chamber 23 of the air timing switch 14.

The restrictors 364, 365 are so chosen that, when the engine is operating under light load conditions (that is, when there is a comparatively high depression downstream of the throttle valve 1 I the depression at the check valve inlet 361 is higher than the depression in the chamber 23 of the air timing switch 14 as transmitted through the line 300 from the control depression region of the air intake conduit 10. The check valve 360 accordingly remains closed. Under high engine load conditions, however, the depression downstream of the throttle valve 11 drops to a comparatively low value and the restrictors 364, 365 are such that the depression at the check valve inlet 361 is then lower than the depression in the chamber 23 of the air timing switch. As a result, air flows through the check valve 360 and reduces the depression in the air timing switch chamber 23 so that the injector devices remain open for a greater length of time.

The systems described above may be modified in various ways. For example, although" the frequency control portion of the switching unit 8 has been described in each case as generating electrical signals in dependence on-engine speed, this is not essential: the frequency control portion of the unit 8 could, for exam ple, function to generate electrical signals at constant intervals (that is, at a constant rate, independent of engine speed). To this end, the stages of the frequency control could be replaced in a suitable manner by a conventional astable multivibrator stage operable to generate pulses at a constant frequency.

The use of the particular forms of air valve mechanisms described are also not essential. The eccentrically-mounted air valve 12 shown in FIGS. 1, 6 and 7 could, for example, be replaced by a centrallymounted valve associated with an external control mechanism which senses the depression between the air valve and the throttle valve 1 1 and is coupled to the air valve through a suitable form of servomechanism as in FIG. 8. Alternative arrangements of this type, which could also be used and in which the servo-mechanism is, in one case, vacuum operated and, in another case, operated by fuel pressure, are described in the complete specification of our copending U. S. Pat. applications Ser.No. 31,315, now abandoned and Ser. No. 31,3l6, now U.S. Pat. No. 3,650,258, filed Apr. 23, 1970. Similarly, the servomechanism 307 and sensing valve 312 shown in FIG. 8 could be replaced by one of the arrangements disclosed in this copending application or, alternatively, the centrally-mounted air valve 12 shown in FIG. 8 could be replaced by an eccentrically-mounted valve as shown in FIG. 1.

It will also be appreciated that the power enrichment valve 304 shown in FIG. 8 or the power enrichment check valve 360 shown in FIG. could, if desired, be replaced by a switch similar to the enrichment switch 212 shown in FIG. 1, with the associated circuitry 211 being incorporated in the switching unit 8. Similarly, the power and cold-start enrichment valves 304, 360, 302, the fuel cut-off switch 303 or the enrichment check valve 360 shown in FIGS. 8 and 10 could be utilized in the system shown in FIG. 1.

Finally, although the use of a plurality of injector devices 5, each incorporating a respective solenoidoperated interrupter valve 142, 146, has been described, this is not essential to the operation of the systems. The plurality of solenoid-operated injectors could, for example, be replaced by a plurality of open injector nozzles associated with a single solenoidoperated interrupter valve which controls fuel flow to the nozzles through respective pressure-responsive control valves, in the manner disclosed in our U. S. application Ser.No. 91,937, filed Nov. 23, 1970 now abandoned.

Iclaim:

1. A fuel injection system for an internal combustion engine, including at least one fuel injector nozzle and at least one interrupter valve connected to control fuel flow through the nozzle(s); an air valve mechanism which includes an air valve located in the engine air intake path to produce a control pressure differential over a region of the air intake path, and which is operable in response to a variation in the control pressure differential from a desired value to adjust the air valve to return the control pressure differential to the desired value; a control fluid flow line to which the air valve is coupled whereby the rate of flow of control fluid through the line varies in response to adjustment of the air valve, and an interrupter valve control mechanism which is cyclically operable to actuate the interrupter valve(s) and then, after a period of time in each cycle determined by the rate of flow of the control fluid, to terminate actuation of the interrupter valve(s).

2. A system as claimed in claim 1, in which the control fluid isair.

3. A system as claimed in claim 2, in which the control fluid flow line is connected to the control pressure differential region.

4. A system as claimed in claim 2, in which the control fluid flow line is connected to feed air into the control pressure differential region from an air supply source.

5. A system as claimed in claim 4, in which the air supply source is the atmosphere.

6. A system as claimed in claim 1, in which the control fluid is fuel.

7. A system as claimed in claim 6, including a fuel supply source for the injector nozzle(s), the control fluid flow line being connected to receive fuel from and return fuel to the said fuel supply source.

8. A system as claimed in claim 6, including means operable to pressurize the control fluid in dependence on the control pressure differential.

9. A system as claimed in claim 1, in which the air valve is coupled to an adjustable flow restrictor in the control fluid flow line 10. A system as claimed in claim 1, in which the interrupter valve control mechanism includes a frequency control which is cyclically operable to actuate the interrupter valve(s) at a frequency dependent on engine speed. 7

11. A system as claimed in claim 1, in which the interrupter valve control mechanism includes a frequency control which is cyclically operable to actuate the interrupter valve(s) at a constant frequency.

12. A system as claimed in claim 1, including a flow control valve connected in the control fluid flow line and operable to change the flow resistance of the flow line and thereby produce a variation in control fluid pressure, at a point in the flow line, at a rate determined by the rate of flow of control fluid, the interrupter valve control mechanism including a frequency control which is cyclically operable to actuate the interrupter valve(s) and also to operate the flow control valve, and a pressure-responsive control which is operable to terminate actuation of the interrupter valve(s) in response to a predetermined value of control fluid pressure at the said point in the flow line.

13. A system as claimed in claim 12, in which the frequency control is operable to closethe interrupter valve(s) to terminate fuel flow through the injector nozzle(s), and to close the flow control valve, and the pressure-responsive control is operable to open the interrupter valve(s) and the flow control valve.

14. A system as claimed in claim 12, in which the frequency control is operable to open the interrupter valve(s) to permit fuel flow through the injector nozzle(s) and to open the flow control valve, and the pressure-responsive control is operable to close the interrupter valve(s) and the flow control valve.

15. A system as claimed in claim 12, in which the frequency control is operable to actuate the interrupter valve(s) simultaneously with operation of the flow control valve.

16. A system as claimed in claim 13, including an enrichment control which is operable to delay closure of the interrupter valve(s) relative to operation of the flow control valve. 

1. A fuel injection system for an internal combustion engine, including at least one fuel injector nozzle and at least one interrupter valve connected to control fuel flow through the nozzle(s); an air valve mechanism which includes an air valve located in the engine air intake path to produce a control pressure differential over a region of the air intake path, and which is operable in response to a variation in the control pressure differential from a desired value to adjust the air valve to return the control pressure differential to the desired value; a control fluid flow line to which the air valve is coupled whereby the rate of flow of control fluid through the line varies in response to adjustment of the air valve, and an interrupter valve control mechanism which is cyclically operable to actuate the interrupter valve(s) and then, after a period of time in each cycle determined by the rate of flow of the control fluid, to terminate actuation of the interrupter valve(s).
 2. A system as claimed in claim 1, in which the control fluid is air.
 3. A system as claimed in claim 2, in which the control fluid flow line is connected to the control pressure differential region.
 4. A system as claimed in claim 2, in which the control fluid flow line is connected to feed air into the control pressure differential region from an air supply source.
 5. A system as claimed in claim 4, in which the air supply source is the atmosphere.
 6. A system as claimed in claim 1, in which the control fluid is fuel.
 7. A system as claimed in claim 6, including a fuel supply source for the injector nozzle(s), the control fluid flow line being connected to receive fuel from and return fuel to the said fuel supply source.
 8. A system as claimed in claim 6, including means operable to pressurize the control fluid in dependence on the control pressure differential.
 9. A system as claimed in claim 1, in which the air valve is coupled to an adjustable flow restrictor in the control fluid flow line
 10. A system as claimed in claim 1, in which the interrupter valve control mechanism includes a frequency control which is cyclically operable to actuate the interrupter valve(s) at a frequency dependent on engine speed.
 11. A system as claimed in claim 1, in which the interrupter valve control mechanism includes a frequency control which is cyclically operable to actuate the interrupter valve(S) at a constant frequency.
 12. A system as claimed in claim 1, including a flow control valve connected in the control fluid flow line and operable to change the flow resistance of the flow line and thereby produce a variation in control fluid pressure, at a point in the flow line, at a rate determined by the rate of flow of control fluid, the interrupter valve control mechanism including a frequency control which is cyclically operable to actuate the interrupter valve(s) and also to operate the flow control valve, and a pressure-responsive control which is operable to terminate actuation of the interrupter valve(s) in response to a predetermined value of control fluid pressure at the said point in the flow line.
 13. A system as claimed in claim 12, in which the frequency control is operable to close the interrupter valve(s) to terminate fuel flow through the injector nozzle(s), and to close the flow control valve, and the pressure-responsive control is operable to open the interrupter valve(s) and the flow control valve.
 14. A system as claimed in claim 12, in which the frequency control is operable to open the interrupter valve(s) to permit fuel flow through the injector nozzle(s) and to open the flow control valve, and the pressure-responsive control is operable to close the interrupter valve(s) and the flow control valve.
 15. A system as claimed in claim 12, in which the frequency control is operable to actuate the interrupter valve(s) simultaneously with operation of the flow control valve.
 16. A system as claimed in claim 13, including an enrichment control which is operable to delay closure of the interrupter valve(s) relative to operation of the flow control valve.
 17. A system as claimed in claim 16, in which the length of the delay varies with adjustment of the engine air control.
 18. A system as claimed in claim 10, in which the, or each, interrupter valve is electromagnetically-operable and the frequency control is cyclically operable to generate electrical signals to actuate the interrupter valve(s).
 19. A system as claimed in claim 12, in which the interrupter valve(s) and the flow control valve are electromagnetically-operable and the frequency control is cyclically operable to generate electrical signals to actuate the interrupter valve(s) and to operate the flow control valve.
 20. A system as claimed in claim 19 in which the pressure-responsive control is operable to generate an electrical signal to terminate actuation of the interrupter valve(s).
 21. A system as claimed in claim 12, in which the pressure-responsive control includes a fluid pressure-responsive electrical switch having a fluid-pressure responsive element exposed to the control fluid pressure at the said point in the control fluid flow line.
 22. A system as claimed in claim 21, in which the pressure-responsive element is a resilient diaphragm which is operably-coupled to a switch contact and one side of which is exposed to the control fluid pressure at the said point in the control fluid flow line.
 23. A system as claimed in claim 12, in which the control fluid is air and in which the said predetermined value of control fluid pressure is adjustable.
 24. A system as claimed in claim 23, in which the pressure-responsive control is also responsive to a biasing pressure whereby variations in the biasing pressure adjust the said predetermined value.
 25. A system as claimed in claim 24, in which the biasing pressure varies with the control pressure differential whereby the said predetermined value is adjusted in response to variations in the control pressure differential to compensate for variations in the rate of flow of the control fluid resulting from those variations.
 26. A system as claimed in claim 25, in which the pressure-responsive control includes a resilient diaphragm one side of which is exposed to the control fluid pressure at the said point in the control fluid flow line and the other side of which is exposed to the pressure in a chamber coNnected through respective fixed restrictors, to the control pressure differential region and to a constant air pressure source.
 27. A system as claimed in claim 26, in which the constant air pressure source is the atmosphere.
 28. A system as claimed in claim 24, including at least one enrichment valve operable to adjust the biasing pressure and thereby adjust the period of time for which the or each, interrupter valve is actuated.
 29. A system as claimed in claim 26, including at least one enrichment valve operable to connect the chamber to an overriding pressure source.
 30. A system as claimed in claim 29, in which the overriding pressure source is the atmosphere.
 31. A system as claimed in claim 28, in which the enrichment valve is operable to adjust, simultaneously, the quantity of air taken in by the engine.
 32. A system as claimed in claim 28, in which the enrichment valve is operable to provide a by-pass air intake path.
 33. A system as claimed in claim 28, in which the enrichment valve is manually operable.
 34. A system as claimed in claim 28, in which the enrichment valve is operable in response to a predetermined engine intake manifold vacuum.
 35. A system as claimed in claim 34 in which the enrichment valve includes a pressure-responsive resilient diaphragm exposed to intake manifold vacuum.
 36. A system as claimed in claim 34, in which the enrichment valve is a pressure-responsive check valve having an inlet connected in a flow line which connects the intake manifold to an overriding pressure source, and an outlet connected to the chamber whereby operation of the check valve connects the chamber to the overriding pressure source.
 37. A system as claimed in claim 1, including a fuel cut-off control operable to terminate cyclic operation of the interrupter valve control mechanism and thereby terminate the supply of fuel to the engine.
 38. A system as claimed in claim 1, in which the air valve is an eccentrically-mounted butter fly valve and the air valve mechanism includes restoring means acting on the air valve in opposition to the control pressure differential.
 39. A system as claimed in claim 1, in which the air valve mechanism includes a fluid pressure-operated servomechanism to which the air valve is coupled, and a sensing valve responsive to a variation in the control pressure differential to adjust the servomechanism.
 40. A fuel injection system for an internal combustion engine, including at least one fuel injector nozzle and at least one interrupter valve connected to control fuel flow through the nozzle(s); an air valve mechanism which includes an air valve located in the engine air intake path to produce a control pressure differential over a region of the air intake path, and which is operable in response to a variation in the control pressure differential from a desired value to adjust the air valve to return the control pressure differential to the desired value; a flow line connected to feed air into the control pressure differential region from the atmosphere; an adjustable restrictor connected in the flow line and coupled to the air valve whereby the rate of air flow through the line varies in response to adjustment of the air valve, and an interrupter valve control mechanism including a frequency control which is cyclically operable to actuate the interrupter valve(s) at a frequency dependent on engine speed and a flow rate responsive control which is operable, at a time in each cycle determined by the rate of air flow in the said flow line, to terminate actuation of the interrupter valve(s).
 41. A system as claimed in claim 40, including a flow control valve connected in the said flow line and operable by the said frequency control to produce a variation in air pressure, at a point in the flow line, at a rate determined by the rate of air flow through the line, the said flow rate responsive control being operable in response to a predetermined value of air pressure at the said point.
 42. A system as claimeD in claim 41, in which the flow rate responsive control is also responsive to the control pressure differential whereby the said predetermined value of air pressure is adjusted in response to variations in the control pressure differential to compensate for variations in the rate of air flow through the said flow line resulting from those variations. 